In order to withdraw a minimal amount of blood from body parts (generally, a finger or an ear lobe) for analytical-diagnostic purposes, lancets are used, which are pricked into the corresponding body part for producing a wound. Because this procedure is manually performed, specially trained personnel are necessary. However, the puncture is connected with substantial pain.
Blood removal systems which comprise a pricking apparatus and associated lancets, specially adapted to the lancets, have also been used. In a housing of the pricking apparatus, a lancet drive is located, by means of which a lancet is mechanically stuck into the skin. A spring serves as a driving element for the puncturing movement. At the beginning of the development, very simple constructions were used, in which the lancet was directly attached to an end of a compression spring arranged in an elongated housing (for example, U.S. Pat. No. 4,469,110).
These types of blood removal system were, however, not suitable to meet the high demands required when a routine monitoring of analytical values of blood is necessary. This is particularly true for diabetics, who must control their blood sugar levels frequently, in order to maintain their blood sugar levels as constant as possible within predetermined nominal limits by means of adapting insulin injections to the requirements (which, depending on the nutrient absorption, the bodily activity, etc., can vary strongly). By comprehensive scientific research, it was demonstrated that by means of an intensive therapy with at least four blood analyses per day, a dramatic decrease of the most severe consequences of diabetes mellitus (for example, a retinal pathology with resulting blindness of the patient) can be achieved.
This intensive therapy requires that the blood removal is connected with the least possible pain. Numerous different blood removal systems were developed with the aim to achieve this goal.
A blood removal with very little pain is achieved by blood removal systems, whose lancet drive includes a drive rotor, which on one side (the input side) is coupled with the drive spring in such a manner that it can be driven thereby to rotate about an axis of rotation. On the other side (output side) it is coupled via a coupling mechanism with the lancet, in such a manner that the rotation of the drive rotor resulting from the tension releasing movement of the drive spring is converted to a puncturing movement whereby the lancet is moved with high speed, until its point or tip exits from the exit opening, thereby producing a wound in the body part which is pressed against a contact surface surrounding the exit opening. The lancet is guided by a lancet guide on a predetermined (in practice, straight) puncture path.
A blood lancet device with such a rotor drive is described in U.S. Pat. No. 4,924,879. Its rotor is driven by means of a coaxial helical spring. The rotational movement of the rotor is converted into the required linear movement of the lancet via a con-rod drive.
In U.S. Pat. No. 5,318,584, a blood removal system is described, which, likewise, operates with a rotor drive. The drive rotor of this system rotates about an axis of rotation, which coincides with the axis of the longitudinally extending, “pencil-shaped” apparatus. A rotational spring that is coaxial with the rotor serves as the drive. The output-side coupling mechanism for converting the rotational movement into the translation movement of the lancet is formed by a curve controller. The form of the control curve makes it possible to cock the apparatus, without the lancet tip exiting from the housing. The rotation of the rotor part about the longitudinal axis of the apparatus leads to very little vibration and stabilizes the puncturing process. A newer version of a blood removal system with a drive rotor that rotates about the apparatus longitudinal axis is described in EP 1034740 A1.
A further embodiment of a rotor drive is described in EP 1090584 A2, in which a drive rotor is used, which rotates about an axis that runs transverse to the direction of puncture. Here the rotation of the drive rotor is caused by the force of the drive spring pressing against a specially formed pressure surface of the rotor. In this manner, it is possible that the rotor rotates in the same direction of rotation both during cocking as well as upon tension release of the lancet drive. Also in this case, the output-side coupling mechanism preferably comprises a curve controller. The construction requires fewer components than the previously discussed rotor drive. It requires, however, a relatively wide housing shape, which is considered less favorable by many users.
In spite of the extensive development work, which has led to the previously discussed and numerous further designs, a large interest exists in a blood removal system, which, at the same time, fulfills, to the extent possible, the difficult and partially opposing requirements (minimal pain, simple operation, compact, most slim structure, and simple, cost-effective construction).